1. Field of the Invention
The present invention relates to an optometric apparatus for subjectively examining (measuring) a refractive power of an eye of an examinee.
2. Description of Related Art
There has been known an optometric apparatus constructed to subjectively examine (measure) a refractive power (a visual acuity) of an eye of an examinee by presenting optotypes forward of the eye through an optical element such as a spherical lens and cylindrical lens placed in front of the eye. Examinations using this type of optometric apparatus include a far vision examination in which optotypes are presented at a far vision examination distance of for example 5 m and a near vision examination in which optotypes are presented at a near vision examination distance of for example 35 cm.
In the case of the near vision examination using the conventional optometric apparatus, a pair of lens chamber units for right and left eyes in each of which optical elements are placed is moved (slid) closer to or away from each other and converged, according to a pupillary distance (PD) of the examinee and a presenting distance (the near vision examination distance) of each optotype. The optometric apparatus provided with such slide mechanism and convergence mechanism can be adjusted to align the optical axis of the optical element disposed in front of the examinee's eye with a visual axis of the examinee's eye in the near vision examination. Accordingly, a prismatic effect by the optical element can be reduced, thus providing examination results with high precision.
The optometric apparatus provided with the above mentioned slide mechanism and convergence mechanism has such a disadvantage that when the right and left lens chamber units are moved closer and converged in order to adjust the optical axis of the optical element to the visual axis of an examinee whose pupillary distance is narrow (short), the lens chamber units are likely to come into contact with each other. The apparatus has been adapted to inhibit sliding and converging of the lens chamber units in the case of such examination conditions that may cause the above contact. However, with this apparatus, the examinations could not be performed with high precision.